Question

A galvanometer of resistance 20 ohms requires a
current of 6mA for full scale deflection. How
do you modify it to measure a potential
difference of 3 volts ?​

Answer 1

Solution:

Voltmeter are made by connecting a large  shunt resistance S in series with the galvanometer.

Let I be the current to produce full scale deflection  

G is the resistance of the galvanometer

V be the maximum value of your required range  

The value of S is given by

S = (V/I) -G

I = 6 mA , V = 3 V and G = 20 Ω.

Then the required value of resistance is

R = [(6/3 × $10^{-3}$)-20]Ω

= 2000 - 20 Ω

= 1980 Ω

Answer 2

Answer:

480

Explanation:

S=(V/I)-G

(3/6x10^-3)-20

(1000/2)-20

500-20

480